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ndemou
Asked: 2014-06-04 07:20:04 +0800 CST

How to write rules for persistent net names?

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I know that a process generates persistent network card names based on rules found in /lib/udev/rules.d/75-persistent-net-generator.rules. I also know how to completely disable this process with a simple 

echo '#' > /etc/udev/rules.d/75-persistent-net-generator.rules

but I've read that I "could also write my own rules file to give the interface a name — the persistent rules generator ignores the interface if a name has already been set" (/etc/udev/rules.d/README confirms that this is possible).

Can you provide instructions and/or examples on how to write such rules? (I mostly care about Debian/Ubuntu and a bit less for CentOS). In my case I would like to add rules like the following:

  • cards with MAC A or B should be named eth0
  • cards with MAC C or D should be named eth1
  • follow default naming scheme for anything else

As a specific example of why I want to write custom rules: I have two identical servers with one onboard LAN and one PCI LAN. In case of HW failure I want to be able to move disks from HW#1 to HW#2 and it's important for eth0 to continue pointing to the onboard card and eth1 to the PCI card (no one wants to mess with cabling in the middle of a HW failure panic). My current workaround works but is a lot of work[1] so I wonder if writing custom rules would allow me to express the above rules

[1] install the OS in HW#1 and keep a copy of /etc/udev/rules.d/70-persistent-net.rules. Move the disks to HW#2 and keep a second copy of the same file. Concatenate the two copies and manually edit the NAME="ethX" part. Replace /etc/udev/rules.d/70-persistent-net.rules with my version. Finally disable auto-creation of a new 70-persistent-net.rules using 

echo '#' > /etc/udev/rules.d/75-persistent-net-generator.rules
linux

2 Answers

  1. Best Answer

    To answer your specific question, add this to persistent-net.rules:

    SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="AA:AA:AA:AA:AA:AA", ATTR{dev_id}=="0x0", ATTR{type}=="1", NAME="eth0"
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="BB:BB:BB:BB:BB:BB", ATTR{dev_id}=="0x0", ATTR{type}=="1", NAME="eth0"
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="CC:CC:CC:CC:CC:CC", ATTR{dev_id}=="0x0", ATTR{type}=="1", NAME="eth1"
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="DD:DD:DD:DD:DD:DD", ATTR{dev_id}=="0x0", ATTR{type}=="1", NAME="eth1"

    Leave persistent-net-generator.rules alone. udev will not overwrite the rules you added manually but the generator rules will cause new rules to be added for new cards as usual.

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  2. Usually all I want to do in terms of naming interfaces is to swap eth0 and eth1. I let the system create the file /etc/udev/rules.d/70-persistent-net-rules, then edit it by switching the names, restart, then configure the interface stanzas in the network config files. Tedious but gets it done. There's a hint at the top of the file about this:

    /etc/udev/rules.d/70-persistent-net.rules 
# This file was automatically generated by the /lib/udev/write_net_rules
# program, run by the persistent-net-generator.rules rules file.
#
# You can modify it, as long as you keep each rule on a single
# line, and change only the value of the NAME= key.

# PCI device 0x8086:0x108c (e1000e) (custom name provided by external tool)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:25:90:22:74:24", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"
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